Heater and image forming apparatus

Abstract

To provide a heater that can prevent the occurrence of warpage in the heater and can prevent an increase in the heat capacity of the heater, and an image forming apparatus.SOLUTION: A heater according to an embodiment is provided with: a substrate that includes metal and has a shape extending toward one side; an insulating layer that is provided on a first surface of the substrate; heating elements that are provided on the insulating layer and extend in a longitudinal direction of the substrate; a protection part that is provided on the insulating layer and covers the heating elements; and a warpage relaxation part that is provided on a second surface of the substrate opposite to the first surface, and the heater satisfies the following formulas: αb<αa; and Tb<Ta. αa (×10-7(1 / °C)) is the coefficient of linear expansion of a material of the protection part. αb (×10-7(1 / °C)) is the coefficient of linear expansion of a material of the warpage relaxation part. Ta (mm) is the thickness of the protection part. Tb (mm) is the thickness of the warpage relaxation part.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] An embodiment of the present invention relates to a heater and an image forming apparatus. [Background technology]

[0002] For example, image forming devices such as copiers and printers are provided with heaters for fixing toner. In general, such heaters include a long substrate, a heating element provided on one surface of the substrate and extending in the longitudinal direction of the substrate, and a protective portion provided on the other surface of the substrate to cover the heating element.

[0003] The substrate is made of a material that is heat resistant and has high thermal conductivity. The protective portion is made of a material that has heat resistance, insulating properties, high thermal conductivity, and high chemical stability, for example, glass.

[0004] Here, if the material of the substrate is a metal, it is possible to improve the rigidity of the substrate and reduce the manufacturing cost. However, if the material of the substrate is a metal, the material of the substrate and the material of the protective part are different, and thermal stress occurs due to the difference in the linear expansion coefficient of the materials. Therefore, if the material of the substrate is a metal, there is a risk that the heater will be significantly warped when it is used or manufactured.

[0005] For this reason, a technology has been proposed in which a warpage mitigation part containing the same material as the protective part is provided on the other side of the substrate (the side opposite to the side on which the protective part is provided). If a warpage mitigation part is provided, the thermal stress generated on one side of the substrate can be offset by the thermal stress generated on the other side of the substrate. Therefore, it is possible to suppress the occurrence of warpage in the heater when the heater is used or when the heater is manufactured.

[0006] However, simply providing a warp mitigating portion increases the heat capacity of the heater, which means that it takes longer for the heater to heat up or cool down. Therefore, there has been a demand for development of a technique capable of suppressing the occurrence of warping in the heater and suppressing the increase in the heat capacity of the heater. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-240606 A Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide a heater and an image forming apparatus that can suppress the occurrence of warping in the heater and can suppress an increase in the heat capacity of the heater. [Means for solving the problem]

[0009] The heater according to the embodiment comprises a substrate including a metal and having a shape extending in one direction; an insulating layer provided on a first surface of the substrate; a heating element provided on the insulating layer and extending in the longitudinal direction of the substrate; a protective portion provided on the insulating layer and covering the heating element; and a warpage mitigation portion provided on a second surface of the substrate opposite the first surface, and satisfies the following formula: αb<αa, Tb <Ta αa(×10 -7 (1 / °C) is the linear expansion coefficient of the material of the protective portion, αb(×10 -7 (1 / °C) is the linear expansion coefficient of the material of the warp mitigation portion, Ta (mm) is the thickness of the protective part, Tb (mm) is the thickness of the warp mitigation portion. Effect of the Invention

[0010] According to an embodiment of the present invention, it is possible to provide a heater and an image forming apparatus that can suppress the occurrence of warping in the heater and the increase in the heat capacity of the heater. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic front view illustrating the heater according to the present embodiment. [Diagram 2] FIG. 4 is a schematic rear view illustrating the heater. [Diagram 3] 2 is a schematic cross-sectional view of the heater in the direction of line AA in FIG. 1. [Figure 4] 11 is a table illustrating the relationship between the thickness of the protective portion, the linear expansion coefficient of the material of the protective portion, the thickness of the warp mitigation portion, and the linear expansion coefficient of the material of the warp mitigation portion, and the occurrence state of warping. [Diagram 5] 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention; [Figure 6] 3A and 3B are schematic diagrams for illustrating a fixing unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment will be illustrated with reference to the drawings. In each drawing, the same components are given the same reference numerals, and detailed description will be omitted as appropriate. In each drawing, arrows X, Y, and Z represent three mutually orthogonal directions. For example, the longitudinal direction of the substrate is the X direction, the short side direction (width direction) of the substrate is the Y direction, and the direction perpendicular to the substrate surface is the Z direction.

[0013] (heater) FIG. 1 is a schematic front view illustrating a heater 1 according to the present embodiment. FIG. 1 is a view of the heater 1 as seen from the side where the heat generating portion 20 is provided. FIG. 2 is a schematic rear view illustrating the heater 1. As shown in FIG. FIG. 2 is a view of the heater 1 as viewed from the side where the warp mitigating portion 50 is provided (the side opposite to the side where the heat generating portion 20 is provided). FIG. 3 is a schematic cross-sectional view of the heater 1 in FIG. 1 taken along the line AA. As shown in FIGS. 1 to 3, the heater 1 includes a substrate 10, an insulating layer 11, a heat generating portion 20, a wiring portion 30, a protective portion 40, and a warpage mitigating portion 50, for example.

[0014] The substrate 10 is plate-shaped and has a surface 10a (corresponding to an example of a first surface) and a surface 10b (corresponding to an example of a second surface) opposite to the surface 10a. The substrate 10 has a shape extending in the X direction. The shape of the substrate 10 as viewed from the Z direction is, for example, a long rectangular shape. The thickness of the substrate 10 is, for example, about 0.5 mm to 1.0 mm. The dimensions of the substrate 10 in the X direction and the dimensions of the substrate 10 in the Y direction can be appropriately changed depending on the size of the object to be heated (for example, paper) and the like.

[0015] The substrate 10 is made of a material having heat resistance and high thermal conductivity, and can be made of a metal such as stainless steel or an aluminum alloy.

[0016] The thermal conductivity of metals is higher than that of inorganic materials such as ceramics. Therefore, if the substrate 10 is made of a metal, it is possible to suppress the occurrence of in-plane distribution of the temperature of the heater 1. In addition, it is possible to improve the rigidity of the substrate 10 and reduce the manufacturing cost.

[0017] The insulating layer 11 is provided on the surface 10a of the substrate 10 on which the heat generating portion 20 is provided. The insulating layer 11 covers the area of ​​the surface 10a of the substrate 10 on which the heat generating portion 20 is provided. The insulating layer 11 is made of a material having heat resistance and insulating properties. The material of the insulating layer 11 and the linear expansion coefficient of the material of the insulating layer 11 will be described later.

[0018] The heat generating portion 20 converts the applied power into heat (Joule heat). The heat generating portion 20 is provided on an insulating layer 11. The heat generating portion 20 and the substrate 10 are insulated from each other by the insulating layer 11. The heat generating section 20 has, for example, a heat generating element 21 and a heat generating element 22. Although the case where the heat generating element 21 and the heat generating element 22 are provided has been illustrated as an example, the number and size of the heat generating elements can be appropriately changed depending on the size of the substrate 10 and the size of the object to be heated. Also, multiple types of heat generating elements with different lengths, widths, shapes, etc. can be provided. That is, it is sufficient that at least one heat generating element is provided.

[0019] Heating element 21 and heating element 22 can be arranged, for example, at a predetermined interval in the Y direction (short side direction of substrate 10). Heating element 21 and heating element 22 extend, for example, in the X direction (longitudinal direction of substrate 10).

[0020] The dimensions (length dimensions) of the heating elements 21 and 22 in the X direction can be, for example, approximately the same. In this case, it is preferable that the centers of the heating elements 21 and 22 are located on the straight line 1a. In other words, it is preferable that the heating elements 21 and 22 each have a shape that is line-symmetrical with respect to the straight line 1a.

[0021] When the heater 1 is attached to the image forming apparatus 100, for example, the straight line 1a is aligned with the center line of the transport path of the object to be heated. In this way, even if the size of the object to be heated in the direction perpendicular to the transport direction changes, the object to be heated can be heated approximately uniformly.

[0022] The electric resistance values ​​of the heating element 21 and the heating element 22 can be approximately the same or different. For example, the electric resistance values ​​of the heating element 21 and the heating element 22 can be approximately the same by making the dimensions in the X direction (length dimension), the Y direction (width dimension), and the Z direction (thickness dimension) of the heating element 21 and the heating element 22 approximately the same. Furthermore, by changing at least one of these dimensions, the electric resistance values ​​of the heating element 21 and the heating element 22 can be made different. Furthermore, by changing the material, the electric resistance values ​​of the heating element 21 and the heating element 22 can be made different.

[0023] Furthermore, the electrical resistance value per unit length of the heating element 21 can be approximately uniform in the X direction. For example, the dimension (width dimension) in the Y direction and the dimension (thickness dimension) in the Z direction of the heating element 21 can be approximately constant. The shape of the heating element 21 as viewed from the Z direction can be, for example, approximately rectangular extending in the X direction.

[0024] Furthermore, the electrical resistance value per unit length of the heating element 22 can be approximately uniform in the X direction. For example, the dimension (width dimension) in the Y direction and the dimension (thickness dimension) in the Z direction of the heating element 22 can be approximately constant. The shape of the heating element 22 as viewed from the Z direction can be, for example, approximately rectangular extending in the X direction.

[0025] Heating element 21 and heating element 22 can be formed using, for example, ruthenium oxide (RuO2), a silver-palladium (Ag-Pd) alloy, etc. Heating element 21 and heating element 22 can be formed, for example, by applying a paste-like material onto insulating layer 11 using a screen printing method or the like, and curing it using a baking method or the like.

[0026] The wiring portion 30 is provided on the insulating layer 11 . The wiring section 30 includes, for example, a terminal 31, a terminal 32, a wire 33, a wire 34, and a wire 35.

[0027] The terminals 31 and 32 are provided, for example, near one end of the substrate 10 in the X direction. The terminals 31 and 32 are provided, for example, side by side in the X direction. The terminals 31 and 32 are electrically connected, for example, to a controller 210 of the image forming apparatus 100 (described later) via a connector, wiring, or the like.

[0028] The wiring 33 is provided, for example, in the X direction, on the side of the substrate 10 where the terminal 31 is provided. The wiring 33 extends in the X direction. The wiring 33 is electrically connected to the terminal 31 and an end of the heating element 21 on the terminal 31 side.

[0029] The wiring 34 is provided, for example, in the X direction, near the end of the substrate 10 opposite to the side on which the terminals 31 and 32 are provided. The wiring 34 is electrically connected to the end of the heating element 21 opposite to the wiring 33 side and the end of the heating element 22 opposite to the wiring 35 side.

[0030] The wiring 35 is provided, for example, in the X direction, on the side of the substrate 10 where the terminal 32 is provided. The wiring 35 extends in the X direction. The wiring 35 is electrically connected to the terminal 32 and the end of the heating element 22 on the terminal 32 side.

[0031] The wiring portion 30 (terminals 31, 32, and wires 33 to 35) are formed using a material containing, for example, silver, copper, etc. For example, the terminals 31, 32 and wires 33 to 35 can be formed by applying a paste-like material onto the insulating layer 11 using a screen printing method or the like, and curing it using a baking method or the like.

[0032] The protective portion 40 is provided on the insulating layer 11, and covers the heat generating portion 20 (heat generating element 21 and heat generating element 22) and a part of the wiring portion 30 (wires 33, 34, and 35). In this case, the terminals 31 and 32 of the wiring portion 30 are exposed from the protective portion 40.

[0033] The protective section 40 extends in the X direction. The protective section 40 has, for example, a function of insulating the heat generating section 20 and a part of the wiring section 30, a function of transmitting heat generated in the heat generating section 20, and a function of protecting the heat generating section 20 and a part of the wiring section 30 from external forces, corrosive gases, and the like. The protective section 40 is formed from a material that has heat resistance and insulating properties, and has high chemical stability and thermal conductivity. The protective section 40 is formed from, for example, glass. In this case, the protective section 40 can also be formed using glass to which a filler containing a material with high thermal conductivity, such as aluminum oxide, has been added.

[0034] The heater 1 may further be provided with a detection unit that detects the temperature of the heat generating unit 20 and the temperature of the substrate 10. The detection unit may be, for example, a thermistor. The detection unit may be provided on at least one of the side of the substrate 10 on which the heat generating unit 20 is provided and the side of the substrate 10 opposite to the side on which the heat generating unit 20 is provided. For example, the detection unit and the wiring and terminals electrically connected to the detection unit may be provided on the insulating layer 11. In this case, the detection unit and the wiring may be covered by the protective unit 40. The terminals electrically connected to the detection unit may be exposed from the protective unit 40.

[0035] As described above, the substrate 10 is made of a metal such as stainless steel or an aluminum alloy, while the insulating layer 11 and the protective portion 40 are made of glass or the like. Therefore, the linear expansion coefficient of the material of the substrate 10 is different from the linear expansion coefficient of the material of the insulating layer 11 and the protective part 40. When the heating part 20 is heated during use of the heater 1, the substrate 10, the insulating layer 11, and the protective part 40 are heated. When the heating part 20, the wiring part 30, the insulating layer 11, and the protective part 40 are baked during manufacture of the heater 1, the substrate 10, the insulating layer 11, and the protective part 40 are heated. Therefore, when the heater 1 is used or manufactured, thermal stress occurs due to the difference in the linear expansion coefficient of the materials. When thermal stress occurs on one side of the substrate 10, the heater 1 may be warped.

[0036] In this case, since the linear expansion coefficient of metal is higher than that of glass etc., the heater 1 is likely to warp significantly. Also, if the length of the short side direction (width direction: for example, Y direction) of the substrate 10 is short, the length of the long side direction (for example, X direction) of the substrate 10 is long, or the thickness of the substrate 10 is thin, the heater 1 is likely to warp significantly. If the heater 1 is warped significantly, the distance between the heater 1 and the object to be heated varies, which may result in uneven heating of the object to be heated.

[0037] 2 and 3, the heater 1 is provided with a warpage mitigating portion 50. The warpage mitigating portion 50 is provided on the surface 10b of the substrate 10, which faces the surface 10a. If the warpage mitigating portion 50 is provided on the surface 10b of the substrate 10, the thermal stress generated on the surface 10a side of the substrate 10 can be offset by the thermal stress generated on the surface 10b side of the substrate 10. Therefore, it is possible to suppress the occurrence of warpage in the heater 1 when the heater 1 is used or when the heater 1 is manufactured.

[0038] It is possible to provide at least one warp mitigating portion 50. When providing a plurality of warp mitigating portions 50, for example, the plurality of warp mitigating portions 50 can be arranged side by side in the longitudinal direction (X direction) of the substrate 10. Note that one warp mitigating portion 50 illustrated in FIG. 2 is provided on the surface 10b of the substrate 10.

[0039] Furthermore, the dimension of the warp mitigating section 50 in the short-side direction (Y direction) of the substrate 10 may be the same as the dimension in the short-side direction (Y direction) of the substrate 10, or may be shorter than the dimension in the short-side direction (Y direction) of the substrate 10. Note that the dimension of the warp mitigating section 50 illustrated in FIG. 2 in the short-side direction (Y direction) of the substrate 10 is shorter than the dimension in the short-side direction (Y direction) of the substrate 10.

[0040] That is, the number, arrangement, and dimensions of the warp mitigation portions 50 can be appropriately changed depending on the warp generated in the heater 1. The number, arrangement, and dimensions of the warp mitigation portions 50 can be appropriately determined by, for example, conducting experiments or simulations.

[0041] As described above, if the warpage mitigating portion 50 is provided, it is possible to suppress the occurrence of warpage in the heater 1 when the heater 1 is used or when the heater 1 is manufactured. However, providing the warpage mitigating portion 50 increases the heat capacity of the heater 1. When the heat capacity of the heater 1 increases, new problems arise in that it takes a long time for the heater 1 to increase in temperature or for the heater 1 to cool down.

[0042] In this case, if the thickness of the protective part 40 is reduced, the volume of the protective part 40 can be reduced, and the heat capacity of the heater 1 can be reduced. However, since the protective part 40 covers the heat generating part 20 and the wiring part 30, if the thickness of the protective part 40 is made too thin, the shapes of the heat generating part 20 and the wiring part 30 may be transferred to the surface of the protective part 40, causing unevenness on the surface of the protective part 40. If unevenness occurs on the surface of the protective part 40, the distance between the surface of the protective part 40 and the heated object may vary, causing uneven heating of the heated object. In addition, when the heated object passes through the heater 1, the heated object may get caught on the unevenness on the surface of the protective part 40. Therefore, there is a limit to reducing the heat capacity of the heater 1 by reducing the thickness of the protective part 40.

[0043] In this case, if the linear expansion coefficient of the material of the protective part 40 is close to the linear expansion coefficient of the metal that is the material of the substrate 10, the thermal stress generated between the protective part 40 and the substrate 10 can be reduced. If the generated thermal stress is reduced, the warping generated in the heater 1 will be reduced. If the warping generated in the heater 1 is reduced, it becomes possible to make the warping mitigating part 50 smaller. If the warping mitigating part 50 is reduced, the thermal capacity of the heater 1 can be reduced.

[0044] In this case, if glass with a high linear expansion coefficient is selected as the material for the protective part 40, the linear expansion coefficient of the material for the protective part 40 will be close to the linear expansion coefficient of the metal that is the material for the substrate 10. However, if glass with a high linear expansion coefficient is selected, the surface roughness of the protective part 40 will increase. If the surface roughness of the protective part 40 increases, uneven heating of the object to be heated may occur or the object to be heated may get caught on the protective part 40, similar to the unevenness of the surface of the protective part 40 described above. For this reason, it is difficult to reduce the heat capacity of the heater 1 by changing the material (linear expansion coefficient) of the protective part 40.

[0045] Therefore, the linear expansion coefficient of the material of the warp mitigating portion 50 is set to be lower than that of the material of the protective portion 40. In this way, the difference between the linear expansion coefficient of the material of the warp mitigating portion 50 and that of the metal material of the substrate 10 becomes larger than the difference between the linear expansion coefficient of the material of the protective portion 40 and that of the metal material of the substrate 10. Therefore, the thermal stress generated between the warp mitigating portion 50 and the substrate 10 becomes large, so that the thickness of the warp mitigating portion 50 can be made thin. If the thickness of the warp mitigating portion 50 is made thinner than that of the protective portion 40, the heat capacity of the heater 1 can be made small.

[0046] In this case, if the thickness of the warp mitigating portion 50 is made thin, unevenness is likely to occur on the surface of the warp mitigating portion 50 due to the thermistor provided on the surface 10b of the substrate 10. Furthermore, depending on the material of the warp mitigating portion 50, the surface roughness of the warp mitigating portion 50 may become large. However, since the warp mitigating portion 50 is provided on the side of the substrate 10 opposite the side of the object to be heated, uneven heating of the object to be heated and the object to be heated not being caught by the warp mitigating portion 50 even if unevenness occurs on the surface of the warp mitigating portion 50 or the surface roughness of the warp mitigating portion 50 becomes large.

[0047] For example, the material of the protective portion 40 may be SiO2-B2O3-Al2O3-based glass. In this case, the linear expansion coefficient of SiO2-B2O3-Al2O3-based glass is 70(×10 -7 (1 / ℃)). If the material of the protective part 40 is B2O3-based glass, the ten-point average roughness RzJIS of the surface of the protective part 40 can be set to about 0.3 (μm). If the thickness of the protective part 40 is 0.05 mm or more, the shapes of the heat generating part 20 and the wiring part 30 can be prevented from being transferred to the surface of the protective part 40.

[0048] For example, the material of the warp mitigating portion 50 can be Al2O3-R2O based glass (R2 is an alkali metal). In this case, the linear expansion coefficient of Al2O3-R2O based glass (R2 is an alkali metal) is 30 (×10 -7The warpage mitigating portion 50 may have a thickness of 0.03 mm or less.

[0049] As described above, the linear expansion coefficient of the material of the warp mitigating portion 50 is set to be lower than the linear expansion coefficient of the material of the protective portion 40. In addition, the thickness of the warp mitigating portion 50 is set to be thinner than the thickness of the protective portion 40.

[0050] Next, the relationship between the thickness of the protective portion 40, the linear expansion coefficient of the material of the protective portion 40, the thickness of the warp mitigating portion 50, the linear expansion coefficient of the material of the warp mitigating portion 50, and the occurrence of warping will be described. FIG. 4 is a table illustrating the relationship between the thickness of the protective portion 40, the linear expansion coefficient of the material of the protective portion 40, the thickness of the warp mitigation portion 50, and the linear expansion coefficient of the material of the warp mitigation portion 50, and the occurrence of warping. In FIG. 4, Ta (mm) is the thickness of the protective portion 40. αa is the linear expansion coefficient (×10 -7 (1 / °C)). Tb (mm) is the thickness of the warp mitigation portion 50. αb is the linear expansion coefficient (×10 -7 (1 / ℃)). In this case, as mentioned above, "αb(×10 -7 (1 / ℃))<αa(×10 -7 (1 / ℃)" and "Tb(mm) <Ta(mm)」である。 In addition, when judging the occurrence of warping, a warp amount of 0.5 mm or less is marked as "O", a warp amount of more than 0.5 mm and less than 1.5 mm is marked as "△", and a warp amount of more than 1.5 mm is marked as "X". The material of the substrate 10 is stainless steel, and the thickness of the substrate 10 is 0.5 mm.

[0051] As can be seen from FIG. 4, if "0.85≦(Ta / αa) / (Tb / αb)≦1.15", the occurrence of warping in the heater 1 can be suppressed. Moreover, if "0.90≦(Ta / αa) / (Tb / αb)≦1.10", the occurrence of warping in the heater 1 can be further suppressed.

[0052] In this case, "0.79(mm / 10 -7 (1 / ℃)≦(Ta / αa)≦0.93(mm / 10 -7 If the temperature is set to "1 / °C", it becomes easier to reduce the amount of warping. Also, "0.70 (mm / 10 -7 (1 / ℃)≦(Tb / αb)≦0.97(mm / 10 -7 If the temperature is set to "1 / °C", it becomes easier to reduce the amount of warping.

[0053] Warping of the heater 1 also occurs due to thermal stress occurring between the insulating layer 11 and the substrate 10. In this case, if the linear expansion coefficient of the material of the insulating layer 11 is close to the linear expansion coefficient of the material of the substrate 10, the thermal stress occurring between the insulating layer 11 and the substrate 10 can be reduced. According to the knowledge obtained by the present inventors, when the linear expansion coefficient of the material of the insulating layer 11 is set to αc(×10 -7 (1 / °C)), and the linear expansion coefficient of the material of the substrate 10 is αd(×10 -7 When the relationship is "0.97≦αc / αd≦1.03 (1 / °C)," the amount of warping caused by the thermal stress generated between insulating layer 11 and substrate 10 can be suppressed to a level that does not pose a practical problem. Furthermore, there are no particular limitations on the material of insulating layer 11 as long as it has heat resistance and insulating properties. The thickness of insulating layer 11 can be made thin as long as the insulating properties can be ensured.

[0054] For example, the material of the insulating layer 11 can be Al2O3-RO-based glass (R is an alkaline earth metal). In this case, the linear expansion coefficient of Al2O3-RO-based glass (R is an alkaline earth metal) is 105 (×10 -7 (1 / ° C.) The thickness of the insulating layer 11 can be set to 0.1 mm or less. In this way, the thermal stress generated between the insulating layer 11 and the substrate 10 can be reduced, and the heat capacity of the heater 1 can be reduced.

[0055] (Image forming device) In one embodiment of the present invention, it is possible to provide an image forming apparatus 100 equipped with a heater 1. The above description of the heater 1 and modified versions of the heater 1 (for example, versions in which a person skilled in the art has appropriately added or removed components or modified the design and which have the features of the present invention) can all be applied to the image forming apparatus 100.

[0056] In the following, as an example, the image forming apparatus 100 will be described as a copier. However, the image forming apparatus 100 is not limited to a copier, and may be any apparatus provided with a heater for fixing toner. For example, the image forming apparatus 100 may be a printer or a rewritable card reader / writer.

[0057] FIG. 5 is a schematic diagram illustrating an image forming apparatus 100 according to the present embodiment. FIG. 6 is a schematic diagram illustrating the fixing unit 200. As shown in FIG. As shown in FIG. 5, the image forming apparatus 100 includes, for example, a frame 110, an illumination section 120, an imaging element 130, a photosensitive drum 140, a charging section 150, a discharging section 151, a developing section 160, a cleaner 170, a storage section 180, a conveying section 190, a fixing section 200, and a controller 210.

[0058] The frame 110 is box-shaped and houses therein an illumination section 120, an imaging element 130, a photosensitive drum 140, a charging section 150, a developing section 160, a cleaner 170, part of a storage section 180, a transport section 190, a fixing section 200, and a controller 210. A window 111 made of a light-transmitting material such as glass may be provided on the upper surface of the frame 110. An original 500 to be copied is placed on the window 111. Also, a moving unit for moving the position of the original 500 may be provided.

[0059] The illumination unit 120 is provided near the window 111. The illumination unit 120 has a light source 121, such as a lamp, and a reflecting mirror 122, for example. The imaging element 130 is provided near the window 111 . The photosensitive drum 140 is provided below the illumination unit 120 and the imaging element 130. The photosensitive drum 140 is provided rotatably. On the surface of the photosensitive drum 140, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer is provided. The charging unit 150 , the discharging unit 151 , the developing unit 160 , and the cleaner 170 are provided around the photosensitive drum 140 .

[0060] The storage section 180 has, for example, a cassette 181 and a tray 182. The cassette 181 is detachably attached to one side of the frame 110. The tray 182 is provided on the side of the frame 110 opposite to the side on which the cassette 181 is attached. The cassette 181 stores paper 510 (e.g., blank paper) before copying. The tray 182 stores paper 511 on which a copy image 511a is fixed.

[0061] The transport unit 190 is provided below the photosensitive drum 140. The transport unit 190 transports the paper 510 between the cassette 181 and the tray 182. The transport unit 190 has, for example, a guide 191 that supports the transported paper 510, and transport rollers 192-194 that transport the paper 510. The transport unit 190 can also be provided with a motor that rotates the transport rollers 192-194.

[0062] The fixing unit 200 is provided downstream of the photosensitive drum 140 (on the tray 182 side). As shown in FIG. 6, the fixing unit 200 includes, for example, a heater 1, a stay 201, a film belt 202, and a pressure roller 203. The heater 1 is attached to the stay 201 on the side of the conveyance line for the paper 510. The heater 1 can be embedded in the stay 201. In this case, the side of the heater 1 on which the protective part 40 is provided is exposed from the stay 201.

[0063] The film belt 202 covers the stay 201 on which the heater 1 is provided. The film belt 202 may contain, for example, a heat-resistant resin such as polyimide.

[0064] The pressure roller 203 is disposed so as to face the stay 201. The pressure roller 203 has, for example, a core metal 203a, a drive shaft 203b, and an elastic portion 203c. The drive shaft 203b protrudes from an end of the core metal 203a and is connected to a drive device such as a motor. The elastic portion 203c is disposed on the outer surface of the core metal 203a. The elastic portion 203c is formed from a heat-resistant elastic material. The elastic portion 203c may contain, for example, a silicone resin.

[0065] Controller 210 is provided inside frame 110. Controller 210 has, for example, a calculation unit such as a CPU (Central Processing Unit) and a storage unit in which a control program is stored. The calculation unit controls the operation of each element provided in image forming apparatus 100 based on the control program stored in the storage unit. Controller 210 can also include an operation unit through which a user inputs copying conditions, a display unit that displays the operating state, an error display, and the like. In addition, since known techniques can be applied to the control of each element provided in the image forming apparatus 100, detailed description thereof will be omitted.

[0066] Although some embodiments of the present invention have been illustrated above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. In addition, the above-mentioned embodiments can be implemented in combination with each other.

[0067] Below, supplementary notes regarding the above-described embodiment are given.

[0068] (Appendix 1) A substrate including a metal and having an elongated shape; an insulating layer disposed on a first surface of the substrate; a heating element disposed on the insulating layer and extending in a longitudinal direction of the substrate; a protective portion provided on the insulating layer and covering the heating element; a warp mitigation portion provided on a second surface of the substrate opposite to the first surface; and satisfying the following formula: αb<αa, Tb <Ta αa(×10 -7 (1 / °C) is the linear expansion coefficient of the material of the protective portion, αb(×10 -7 (1 / °C) is the linear expansion coefficient of the material of the warp mitigation portion, Ta (mm) is the thickness of the protective part, Tb (mm) is the thickness of the warp mitigation portion.

[0069] (Appendix 2) 2. The heater of claim 1, further satisfying the following formula: 0.85≦(Ta / αa) / (Tb / αb)≦1.15

[0070] (Appendix 3) 3. The heater according to claim 1 or 2, further satisfying the following formula: 0.90≦(Ta / αa) / (Tb / αb)≦1.10

[0071] (Appendix 4) The heater according to any one of claims 1 to 3, further satisfying the following formula: 0.97≦αc / αd≦1.03 αc(×10 -7 (1 / °C) is the linear expansion coefficient of the material of the insulating layer, αd(×10 -7 (1 / °C) is the linear expansion coefficient of the material of the substrate.

[0072] (Appendix 5) An image forming apparatus comprising the heater according to any one of claims 1 to 4. [Explanation of symbols]

[0073] REFERENCE SIGNS LIST 1 heater, 10 substrate, 10a surface, 10b surface, 11 insulating layer, 20 heat generating portion, 21 heat generating element, 22 heat generating element, 30 wiring portion, 40 protective portion, 50 warping mitigation portion, 100 image forming apparatus, 200 fixing portion

Claims

1. A substrate including a metal and having an elongated shape; an insulating layer disposed on a first surface of the substrate; a heating element disposed on the insulating layer and extending in a longitudinal direction of the substrate; a protective portion provided on the insulating layer and covering the heating element; a warp mitigation portion provided on a second surface of the substrate opposite to the first surface; and satisfying the following formula: αb<αa, Tb<Ta αa (×10 －７ (1 / °C) is the linear expansion coefficient of the material of the protective portion, αb (×10 －７ (1 / °C) is the linear expansion coefficient of the material of the warp mitigation portion, Ta (mm) is the thickness of the protective part, Tb (mm) is the thickness of the warp mitigation portion.

2. 2. The heater of claim 1 further satisfying the following formula: 0.85≦(Ta / αa) / (Tb / αb)≦1.15

3. 3. The heater according to claim 1, further satisfying the following formula: 0.90≦(Ta / αa) / (Tb / αb)≦1.10

4. 3. The heater according to claim 1, further satisfying the following formula: 0.97≦αc / αd≦1.03 αc (×10 －７ (1 / °C) is the linear expansion coefficient of the material of the insulating layer, αd (×10 －７ (1 / ° C.) is the linear expansion coefficient of the material of the substrate.

5. 2. An image forming apparatus comprising the heater according to claim 1.

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